Method of and apparatus for accelerating ions



June 28, 1966 w. s. BANKSTON, JR 3,258,645

METHOD OF AND APPARATUS FOR ACCELERATING IONS Filed March 16, 1964 Fig. la

F/gJb Fig lc M AGENT- E w fim ATTORNEY United States Patent 3,258,645 METHOD OF AND APPARATUS FOR ACCELERATING IONS Weldon S. Bankston, Jr., Miraleste, Califi, assignor, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Filed Mar. 16, 1964, Ser. No. 352,402 6 Claims. (Cl. 315-111) The present invention relates to a simple and effective method and means for generating and accelerating ions or plasma jets. Such apparatus is particularly useful in connection with rocket propulsion systems, nuclear reactors, and for investigating blast effects.

Many devices are known for accelerating the particles of a gas so that they attain relatively high velocities. This is particularly true in nuclear systems, where small quantities of a gas in the form of free ions are repeatedly accelerated until they reach a speed which closely approximates that of light. Despite the high velocity which can be achieved in this manner, these devices are limited to extremely low flow rates by the fact that the ions create a space charge which inherently tends to oppose the accelerating field.

It is also known that relatively large quantities of a gas can .be accelerated to yield much higher flow rates, for example by thermal methods in internal combustion reaction motors, wherein the random velocity of the molecules of a burning gas are converted to a directed velocity by permitting the gas to expand in a properly designed nozzle. However, in these devices the maximum velocity which the gas can attain is limited to a fairly low value by the energy of the fuel and by the fact that the combustion chamber wall must be kept below a temperature at which destruction thereof would occur.

Still another procedure now known for generating extremely high plasma temperatures involves the use of a gas-filled toroid around which a magnetic field winding is placed. According to this technique, the gas in the toroid is ionized, and a circulating current of very high magnitude is induced therein, this circulating current producing what is known as a pinch eifec to constrict the (gas to a toroidal form having as small a volume as possible. While this technique has produced effective temperatures as high as million degrees centigrade, it possesses several disadvantages. Firstly, the maximum temperature obtainable thereby is limited by radiation due to the high inter-particle relative velocities, and, secondly, the gas is trapped in the toroidal chamber and cannot be emitted in high-velocity output bursts. Finally, the temperature is achieved in the center of the gas toroid by radial acceleration of the particles toward the toroidal axis, and this fact limits the practical usefulness of the reaction.

According to a feature of the present disclosure, a device is provided which serves to accelerate ionic particles which are generated by an exploding bridgewire, utilizing a series of axially spaced coils around each of which an electromagnetic field is induced by the same current pulse which is applied to the bridgewire to produce the ionization thereof. These coils are not directly connected to one another in either a physical or an electrical sense, and are so spaced apart that the respective electromagnetic fields built up therein act successively upon the ionic particles emitted during the bridgewire explosion, the generation of these fields occurring in such timed sequence that the ionic particles pass through each coil at the exact time instant when the electromagnetic field developed around such coil is collapsing, thereby adding an accelerating force to the particles as they pass through the winding. A feature of this arrangement is that all of the fields established around the coils result from the same current pulse which initially causes the bridgewire 3,258,645 Patented June 28, 1966 electrical connection between the power source which is utilized to generate the ions and each of the coils by means of which successive accelerating forces are applied thereto.

One object of the present invention, therefore, is to provide an improved method and means for generating and accelerating ions.

Another object of the invention is to provide means for accelerating ionic particles through the action thereon of successive magnetic fields.

A further object of the invention is to employ a pair of axially-spaced coils through which ionic particles are to pass, :and to generate a single current pulse so as to induce magnetic fields of cyclically-recurring magnitude in both coils, the current decay in the first coil initially accelerating the ions, and the current decay in the second coil during the next succeeding cycle imparting a still further acceleration thereto.

Other objects, advantages, and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings wherein:

FIG. 1 is a partly schematic view of a preferred (form of apparatus designed in accordance with the principles of the present invention, and illustrating the manner in which ions are accelerated thereby;

FIG. 2 shows waveforms of the current existing in the apparatus of FIG. 1 at successive inst-ants of time;

FIG. 3 is a side view of a portion of the apparatus of FIG. 1, showing the configuration thereof; and 0 FIG. 4 is an end view of FIG. 3.

Referring now to the drawing, there is shown in FIG. 1(a) a pulse generator 10- which is connected to an explodable bridgewire 12 by a pair Oif parallel conductors 14. Although the characteristics of this bridgewire 12 form no part of the present invention, it might be men- The generator 10 is adapted to produce a single pulse such as indicated by the reference number 16 in FIG 2(a). Although this may be accomplished by many conventional types of circuits, it is preferable that the network 10 include therein a capacitor having a value of approximately two microfarads which is typically charged to about 2 kilovolts. Under the above conditions, the current in the bridgewire circuit which includes the conductors 14 will be in the form of a high initial current pulse 16 (of 1500 to 2000 amperes) followed by a time interval dependent upon the length of the conductors 14 (approximately one microsecond) and then a current restrike across the electrodes of the bridgewire.

In accordance with the present concept, this varying current is employed to accelerate the ions generated by the explosion of the bridgewire 112. In order to carry out this objective, there is provided two coils which are arranged in axial fashion with respect to the bridgewire 12. These coils are designated in FIG. 1 by the reference numerals 18 and 20, respectively, and are so arranged that ions 22 which are generated by the explosion of the bridgewire 12 are successively accelerated through the coils in a manner now to be described.

As shown in FIG. 1, the coil 18 is provided with a pair of terminal conductors 24 which are disposed in parallel relation to the respective bridgewire conductors 14 and closely spaced apart therefrom. In similar fashion, the coil 20 is provided with a pair of terminal conductors 26 which extend respectively parallel both to the con ductors 14 of the bridgewire and also respectively parallel to the conductors 24 of coil 18. When the current pulse 16 is produced by the generator to explode the bridgewire 12, the flow of current through the conductors 14 induces a current in the closely associated conductors 24 and 26, which, in turn, causes electromagnetic fields to be developed around both the coils 18 and 20, as shown in FIG. 1(a). The ions 22 which are generated by the explosion of the bridgewire enter the field of coil 18 at the time instant when this field begins to collapse, or, in other words, at the time instant indicated by the reference numeral 28 in 'FIG. 2(a). This collapsing field in coil 18 exists for the duration of waveform portion 29 (FIG. 2(b)) and accelerates the ions to a location shown in FIG. 1(b).

When the ions 22 have thus reached the position shown in FIG. 2(b) current restrike occurs, and electromagnetic fields are again developed around the coils 18 and 20 as illustrated in FIG. 1(0) due to the rise in current represented by the waveform portion 30 in FIG. 2(c). The distance L between the coils 18 and 20 is so chosen that the ions enter the influence of coil 20 at a time when the electromagnetic field surrounding this coil reaches a maximum, as shown by the reference number 32 in FIG. 2(d). The magnetic field around the coil 20 then collapses, as brought out by the waveform portion 34 in FIG. 2(d), and this collapsing field imparts a further acceleration to the ions, which then assume a location as illustrated in FIG. 1(d). Having received accelerating forces from the two coils 18 and 20, the ions 22 are now traveling at a high velocity, .and are capable of being utilized in the engine of a space vehicle when some known type of automatic wire-feeding device is associated with the electrodes 14 to permit a successive generation of ions in a pulsed manner.

In FIGS. 3 and 4 of the drawings are shown side and end views, respectively, of the coils of FIG. 1. As shown in these figures, the coil 18 is of generally toroidal configuration, while the coil 20 is of oval cross-section. This is because the coil 18 acts not only to accelerate the ions 22 but also to focus them so that they will pass through the coil 20 substantially along the axis thereof.

From the above it will be appreciated that one of the basic features of the present disclosure resides in the elimination of a separate source of energy to accelerate the ions after they have been generated. It should be noted that there is no physical connection among the ionproducing means, the first accelerating coil, and the second accelerating coil. The energy stored in the components themselves is utilized for the purpose of increasing the velocity of the ions, so that the overall efficiency of the apparatus exceeds that which has been reached with designs heretofore known.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

I claim:

1. Apparatus for accelerating ions, said apparatus comprising:

an ionizable element in the form of an explodable whereby, when a single pulse of energy is supplied from said source through said pair of electrodes to explode said bridgewire, .a current will be induced in said conductors to energize said member and cause an electromagnetic field to be developed around the latter, the electromagnetic field thus developed around said member acting to impart an accelerating force to the ions produced by the explosion of said bridgewire as they pass through the influence of said field.

2. Apparatus according to claim 1 in which said pair of electrodes and said pair of conductors are of linear configuration and are disposed in spaced-apart parallel relationship to one another.

3. Apparatus for accelerating ions, said apparatus compr1s1ng:

an ionizable element;

a source of pulse energy;

a pair of electrodes for supplying a single pulse of energy from said source to said element to ionize the latter;

a first energizable member capable of developing an electromagnetic field when energized, said member lying in the path of ions produced by the ionization of said element;

a first pair of conductors connected to said first energizable member;

whereby, when a single pulse of energy is supplied from said source through said pair of electrodes to ionize said element, a current will be induced in said first pair of conductors to energize said member and cause an electromagnetic field to be developed around the latter, the electromagnetic field thus developed around said member acting to impart an accelerating force to the ions produced by ionization of said element as they pass through the influence of said field;

a second energizable member capable of developing an electromagnetic field when energized, said second member lying in the path of ions which have been accelerated by said first energizable member; and

a second pair of conductors connected to said second energizable member;

whereby, when a single pulse of energy is supplied from said source through said pair of electrodes to ionize said element, a current will be induced in said second pair of conductors to energize said second member and cause an electromagnetic field to be developed around the latter, the electromagnetic field thus developed around said second member acting to impart a further accelerating force to the ions accelerated by first member as they pass through the influence of said second field.

4. Apparatus according to claim -3 in which said ionizable element is an explodable bridgewire.

5. Apparatus according to claim 3 in which both said first and second energizable members are in the form of coils through which said ions successively pass.

6. Apparatus according to claim 3 in which said pair of electrodes, said first pair of conductors, and said second pair of conductors are all of linear configuration and are disposed in spaced-apart parallel relationship to one another.

References Cited by the Examiner UNITED STATES PATENTS 10/1962. Salisbury 3l363 X 9/1964 Mayfield 3136'3 X 

1. APPARATUS FOR ACCELERATING IONS, SAID APPARATUS COMPRISING: AN IONIZABLE ELEMENT IN THE FORM OF AN EXPLODABLE BRIDGEWIRE; A SOURCE OF PULSE ENERGY; A PAIR OF ELECTRODES FOR SUPPLYING A SINGLE PULSE OF ENERGY FROM SAID SOURCE TO SAID BRIDGEWIRE TO EXPLODE THE LATTER; AN ENERGIZABLE MEMBER CAPABLE OF DEVELOPING AN ELECTROMAGNETIC FIELD WHEN ENERGIZED, SAID MEMBER LYING IN THE PATH OF IONS PRODUCED BY THE EXPLOSION OF SAID BRIDGEWIRE; AND A PAIR OF CONDUCTORS CONNECTED TO SAID ENERGIZABLE MEMBER; WHEREBY WHEN A SINGLE PULSE OF ENERGY IS SUPPLIED FROM SAID SOURCE THROUGH SAID PAIR OF ELECTRODES TO EXPLODE SAID BRIDGEWIRE, A CURRENT WILL BE INDUCED IN SAID CONDUCTORS TO ENERGIZE SAID MEMBER AND CAUSE AN ELECTROMAGNETIC FIELD TO BE DEVELOPED AROUND THE LATTER, THE ELECTROMAGNETIC FIELD THUS DEVELOPED AROUND SAID MEMBER ACTING TO IMPART AN ACCELERATING FORCE TO THE IONS PRODUCED BY THE EXPLOSION OF SAID BRIDGEWIRE AS THEY PASS THROUGH THE INFLUENCE OF SAID FIELD. 